The present invention relates to the processing of documents and particularly to the serial delivery of envelopes of mixed size and thickness from an unsorted stack to a character reader. More specifically, this invention is directed to a transport system having the capability of accepting, and feeding singly to a character reader, pieces of mail of different sizes received in the form of an unsorted stack. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.